What this calculator does
This tool applies the formulas and tables in Cherokee County's Article 27, Tree Preservation and Replacement, as amended on August 19, 2025. Enter a tree's trunk diameter and type, and it returns three things the ordinance defines: the critical root zone radius and area, the tree's density unit value from Appendix C Table A, and whether its size meets the Appendix A specimen tree threshold.
It does not price any work, and it does not decide whether a tree is protected on your property. Many owners will be exempt from the ordinance entirely; Article 27 exempts tree removal by existing single-family and duplex homeowners, except Heritage Trees. The numbers are still useful: they tell you how much ground to keep machines off when you want a tree to survive nearby work, and they show how the county values trees on sites that are permitted.
Calculator: root zone, density units and specimen size
Formulas: Cherokee County Zoning Ordinance Article 27 (amended Aug. 19, 2025): critical root zone radius 1.5 ft per inch DBH; Appendix C Table A density units (41 in.+ = DBH² × 0.7854 ÷ 144); Appendix A specimen size (overstory 24 in., understory 10 in., pines excluded; condition criteria also apply); Boundary Tree = 10 in. DBH or larger on adjacent property. No prices.
The formulas behind it
Root zone: Article 27 defines the critical root zone as the area beneath a tree that must be left undisturbed to preserve enough root mass to give the tree a reasonable chance of survival. It is drawn as a circle centered on the trunk with a radius in feet equal to one and one-half times the tree's diameter at breast height in inches. Diameter at breast height is measured four and one-half feet above the ground; a trunk that splits lower is measured at its narrowest point beneath the split. The area shown is simply pi times the radius squared.
Density units: Appendix C Table A assigns unit values by size class, from 0.3 units for a 5 to 8-inch tree to 8.1 units for a 37 to 40-inch tree, and trees from 1 to 4 inches need not be counted. For trees of 41 inches or more, the ordinance gives a formula: diameter squared times 0.7854, divided by 144. Specimen size: Appendix A requires 24 inches DBH or larger for overstory trees and 10 inches or larger for understory trees, and states that pine species do not qualify.
| Measure | Value in the ordinance |
|---|---|
| Critical root zone radius | 1.5 feet per inch of DBH |
| DBH measurement height | 4.5 feet above ground |
| Boundary Tree | 10 inches DBH or larger, on adjacent property |
| Specimen size, overstory | 24 inches DBH or larger |
| Specimen size, understory | 10 inches DBH or larger |
| Specimen eligibility, pines | Pine species do not qualify |
| Density units, 41 inches or more | DBH squared x 0.7854 / 144 |
How to measure a tree correctly
Use a tape measure around the trunk at four and one-half feet above the ground, the height Article 27 uses. That gives you circumference. Divide the circumference by pi, about 3.14, to get the diameter. A trunk that measures 63 inches around is about 20 inches in diameter. The calculator wants diameter in inches.
Overstory or understory is about the species, not the individual tree. Article 27 defines overstory trees as species that make up the top canopy layer and generally reach a mature height of more than forty feet; understory trees are the smaller species beneath. The ordinance's Appendix D recommended species list sorts species into those groups: white oak, scarlet oak, southern red oak and American sycamore appear among its overstory trees, while flowering dogwood, eastern redbud and American hornbeam appear among its understory trees. If your species is not obvious, an arborist can tell you.
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Free Quote RequestReading the results
If the calculator says a tree meets the specimen size threshold, that is only half of the test. Appendix A says both size and condition criteria must be met: a life expectancy of more than fifteen years, a relatively sound and solid trunk with no extensive decay, no more than one major and several minor dead limbs, and no major insect or pathological problem, as determined by the county arborist. Our specimen and heritage tree guide explains what follows from that status on permitted sites.
If you are planning work near the tree, mark the root zone radius on the ground with stakes or paint before equipment arrives. Ask your provider to keep trucks, chippers and log piles outside that circle. For boundary trees on a neighbor's land, Article 27 notes that on permitted sites, encroaching on more than ten percent of the root zone requires notice to the tree's owner. See tree removal in Ball Ground for how that fits a removal plan.
Worked examples using the same tables
A 20-inch white oak: root zone radius 30 feet, area about 2,827 square feet, density value 1.9 units (17 to 20-inch class), below the 24-inch overstory specimen threshold. A 26-inch oak: radius 39 feet, density 3.8 units, and its size meets the overstory specimen threshold, subject to the condition criteria.
A 12-inch dogwood: radius 18 feet, density 0.6 units, and its size meets the 10-inch understory threshold. A 30-inch loblolly pine: radius 45 feet and density 5.1 units, but pines do not qualify as specimen trees regardless of size. A 44-inch tree: the formula gives 44 times 44 times 0.7854 divided by 144, about 10.56 units. These examples use the same rules as the tool above.